To see all the Instances of svchost and
how much they consume download the following program and run it. Right click on each instance of svchost and click on
properties.
Download
here: Free - Process Explorer.

Otherwise if you have unusual activities
while the system is idle, and see Unexplainable instances of svchost or other processes, might be that you have a Trojan and other
"Junk" that invoke more instances of svchost and other processes and chokes your system.